Whitening agents for cellulosic fiber



WHITENING AGENTS FOR CELLULOSIC FIBER Arthur A. Baum and Paul A. Sanders, New Casfle County,

Del., assignors to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware No Drawing. Application September 30, 1952, Serial No. 312,412 Claims. (Cl. 260-304) This invention relates to the production of novel organic compounds which are useful as whitening agents for fibrous material such as textiles or paper. It is an object of this invention to produce compounds of the above general nature, but which are characterized further by bleach fastness and by correct shade of fluorescence. Additional objects and achievements of this invention will appear as the description proceeds.

The art of whitening or brightening textile fiber and paper is of relatively recent development. It has been found that fibrous materials which normally have a dull, yellowish cast when in the white, unbleached state, become whiter and brighter if treated with agents which fluoresce under ultraviolet light. Presumably the action of the ultraviolet rays present in ordinary daylight is suflicient to excite these agents upon the fiber to emit fluorescence which overcomes the undesirable tinge of color in the unbleached fiber. Best results are obtained when the shade of fluorescence is complementary to that of the unbleached fiber, so that the colors will cancel out each other. Since the most common otf-white shade of unbleached cellulosic fiber is yellowish, the most desirable shade in a fluorescent is blue. Many fluorescents of green or pink shade have been proposed and tried, but these can be used only in very minute concentration, inasmuch as larger concentrations of these tend to shade the fiber in undesirable green or pink shades. The blue-fluorescents, however, can be used in relatively large concentration (say up to 0.10% by weight of the fiber), and are very effective in producing bright, white textiles.

Another very important demand developed by the trade is bleach fastness. Inasmuch as the aforementioned fluorescent agents are generally incorporated into soap and synthetic detergents, which are packaged and matketed for household use, and inasmuch as in household practice laundered articles are often subjected to bleaching with various agents, for instance hypochlorites, it is essential that the fluorescent transferred from the detergent to the fiber shall not be destroyed by the action of bleach. Unfortunately, most of the fluorescent agents now on the market, and having the desirable blue shade, are weak in respect to this qualification of bleach resistance.

In addition to the above two primary qualifications, an agent to be commercially successful must be capable of being synthesized economically from readily available materials, and must have suflicient fluorescent power (often referred to as tinctorial strength) to give the desired effect at a minimum cost. It must also have affinity for the fiber that is to be treated and must possess suflicient water-solubility to be applicable from an aqueous bath in the concentrations that would normally be used.

Now according to our invention new chemical compounds are synthesized which satisfy to an excellent degree all the aforegoing qualifications. The novel compounds of this invention may be defined by the general formula ADM 2,7i3,054 Patented July 12, 1955 wherein R represents the radical of Z-phenyl-benzothiazole and its homologs or a monosulfo derivative of these, while M stands for hydrogen, an alkali-metal or the ammonium radical.

These compounds may be synthesized by diazotizing 2-(p-aminophenyl)-benzothiazole, dehydro-thio-p-toluidine or dehydro-thio-m-xylidine or their monosulfo derivatives, then coupling (in acid medium) to either 1- aminoor 2-aminonaphthalene-4-sulfonic acid. The resulting ortho-amino azo compound is then converted into a triazole by oxidation in known manner, for instance by heating in an aqueous solution of cupric ammonium sulfate or of sodium hypochlorite until the color of the intermediate azo dye has disappeared, followed by recovery of the product in a desired physical or chemical form, for instance in the form of an alkali-metal or ammonium salt.

Without limiting this invention, the following examples are given to illustrate our preferred mode of operation. Parts mentioned are by weight.

Example 1.-Synthesis 34.2 parts (0.1 mol) of dehydrothio-p-toluidine sodium sulfonate were diazotized, at 05 C., with sodium nitrite and an excess of hydrochloric acid, in 1000 parts of water. A solution of 27 parts of sodium naphthionate (0.11 mol) in 400 parts of water was added. The acidity was reduced by the aid of sodium acetate to a weakly acid test on Congo Red paper, and the mixture was allowed slowly to assume room temperature. The mixture was then made alkaline to Brilliant Yellow paper, and the aminoazo dye was salted out and filtered off.

The wet dye cake thus prepared was dissolved in 2000 parts of water at 60 C. A solution of 50 parts of CuSO4.5l-lz0 in 100 parts of water and 300 parts of concentrated ammonia (28%) was added. The mixture was then heated to reflux for 3 hours and diluted with 1000 parts of water. 24 parts of sodium hydroxide were added, and the mixture was boiled for 1 hour. The solution was filtered hot, clarified while hot with charcoal, then salted out with sodium chloride. The precipitated product was filtered off and dried. It was a light yellow solid, soluble in water with a bright bluish fluorescence.

The product possesses the formula (The location of the SOaNa group in the 2-phenyl-6- methylbenzothiazole complex is'not known with certainty.)

Example Z. Synthesis The procedure of Example 1 was repeated except that the oxidation of the intermediate ortho-amino azo dye was effected by heating the same at 6070 C., for 2 to 3 hours, in an alkaline solution of sodium hypochlorite into which additional sodium hypochlorite was fed at a rate sulficient to maintain a positive test to starch-iodide paper.

After clarification of the solution with charcoal, the product was recovered by salting out, filtering and drying.

Example 3.-Practical application and testing Cotton cloth was washed with a heavy duty detergent containing 80 p. p. m. (based on fabric) of the aforegoiug triaz ole sodium salt.

The heavy duty detergent referred to above was a commercial detergent (such as Tide or "Surf"? composed, by weight, of approximately 30% of the active ingredient (i. e., a long chain alkyl aryl sulfonate), 3% of carboxy methyl cellulose and 68% of sodium polyphosphate.

The treated cloth, which was considerably whiter than the untreated cloth, was then subjected to a bleach-fastness test as follows:

TEST A The treated cloth was entered into an aqueous solution of sodium hypochlorite (in concentration equal to about 0.02% of available chlorine) and stirred therem at 110 F. for minutes. The cloth was then removed, rinsed and dried. No noticeable change in the whiteness of the treated cloth was observed.

To further test the bleach-resistance of the novel compound, the following additional and more rigorous test was carried out:

TEST B An aqueous solution containing by weight 0.4% of a heavy duty detergent (same as above) and 66 p. p. m. (based on the cloth to be treated) of the above triazole sodium salt was heated to 130 F., and sodium hypochlorite was added in quantity calculated to yield a concentration of 0.02% of available chlorine (based on bath weight). Two minutes later, cotton cloth was entered into the dye bath and the temperature of the mixture was maintained at 130 F. for twenty minutes. The cloth was then removed from the dye bath, rinsed. and dried. The cloth thus treated was measured by spectrophotometric methods and found to have 96l00% of the fluorescence produced on a control sample of cloth treated under the same conditions in a similar bath but containing no bleach.

A third sample of cloth. treated under identical conditions in the presence of sodium hypochlorite, but using as fluorescent a present-day commercial product based on diaminostilbene, measured barely 10% of the fluorescence of a fourth piece of cloth (control) treated with the same fluorescent in the absence of bleach.

Tests for light-fastness, substantivity and wash fastness were also carried out, and showed our novel compound to compare favorably in respect to these qualities with the best fluorescents which are now on the market.

If the 34.2 parts of dehydro-thio-p-toluidine sodium sulfonate in the above examples are replaced by 37 parts of dehydro-thio-m-xylidine sodium sulfonate or 3 .8 parts of 2-(p-aminophenyl)-benzothiazole sodium sulfonate. products of similar characteristics are obtained. Essentially similar compounds are also obtained if the respective primary amines free of sulfo groups are employed.

Identically the same compounds. respectively. are obtained when the 1-naphthylamine-4-sulfonie acid above is replaced by 2-naphthylamine-4-sulfonic acid.

The compounds given in the above examples have been isolated as the sodium salts of the sulfonic acids. By using potassium hydroxide and potassium salts in lieu of sodium hydroxide and sodium salts. throughout, the products may be obtained as potassium sulfonates. Isolation as the free sulfonic acids can be effected by acidification of the condensation mass, and the products thus obtained may be reacted with ammonium hydroxide or any suitable organic or inorganic base, to yield the corresponding salt.

In addition to producing a whitening eifect upon textile material or paper, our novel compounds may also be used for various other purposes where fluorescence or absorption of ultra-violet light is desirable, for instance to achieve fluorescent effects in costumes or stage settings, to achieve novel effects on photographic paper, as ultraviolet filters when impregnated on cellulosic films which are used for wrapping materials, etc.

in the claims below, the 4'position of a 2-pheny1 benzothiazole compound shall be understood as referring to the 4'position of the phenyl ring attached in the 2- position of the benzothiazole nucleus, the numbering system assumed being as follows:

We claim as our invention: 1. A compound of the general formula wherein R represents the 4'radical of a 2-phenyl benzothiazole of the group consisting of Z-phenyl-benzothiazole itself, its monomethyl and dimethyl homologs, and the monosulfo derivative of any of these, and wherein M designates a cation of the group consisting of the alkali-metals, ammonium and hydrogen, the attachment of said radical R to the triazole ring shown in the above formula being through the 4'positi0n of its 2-phenyl ring.

2. A compound of the formula NaOJS said compound being a yellowish solid, soluble in water with a bluish fluorescence.

3. The process of producing a fluorescent agent of bluish fluorescence and good bleach-fastness, which comprises diazotizing a p-amino-phenyl-benzothiazole compound ot the group consisting of 2-(p-aminophenyl) benzothiazole, dehydro thio-p-toluidine, dehydro thiom-xylidine and their monosulfo derivatives, coupling the tliazonium compound to a 4-sulfo-naphthalene having a primary amino group in one of the 1,2-positions and a hydrogen atom in the other of said positions, and oxidizing the resulting ortho-amino azo compound to produce in triazole.

4. A process as in claim 3, the oxidation being eftested by heating the compound in an aqueous solution of cupric-ammonium sulfate.

5. A process as in claim 3, the oxidation being effected by heating the compound in an aqueous solution of sodium hypochlorite.

References Cited in the file of this patent UNITED STATES PATENTS 1,149,582 Huismann Aug. 10, 1915 1,871,673 Ellis et a1. Aug. 16, 1932 2,362,988 Conzetti Nov. 21, 1944 FOREIGN PATENTS 4,448 Great Britain 1895 57,557 Germany Sept. 14, 1890 410,857 Great Britain May 28, 1934 

1. A COMPOUND OF THE GENERAL FORMULA 